It's been a while since I have done any Applescript, but I think the problem with your code is, the choose folder command returns an HFS style path as an alias, and you want to pass a POSIX style path as an escaped string to the do shell script command, so you have to convert the returned HFS alias into a POSIX path, and then use the quoted form of command, to convert it into an escaped string, that you then use in the shell script.

Like this example.

Code:

set destinationFolder to choose folder with prompt "Choose the destination folder to save the image file."
set destinationFolderPosixPath to POSIX path of destinationFolder
do shell script "ls " & quoted form of destinationFolderPosixPath